It's at the waistline or just above. The belly button is about right. It's the refs call though. A lot of fighters like to wear their trunks high so they don't have to worry about their trunks sagging. Foreman would wear them almost halfway up his stomach. It's the refs job to identify where the waistline is. Just because you get hit on the trunk belt doesn't mean it's a lowblow and that was definitely the case in the Corley fight.